As the call session control function entity in a IMS network, the operation reliability of the CSCF entity has great significance in the reliable operation of the entire IMS network. In order to guarantee the entire IMS network to operate reliably, ideas of network element availability detection and adjacent network element load balancing selection are provided in the conventional IMS. The idea of the network element availability detection introduces link detection mechanism into the IMS, and the link detection mechanism uses the method of session initiation protocol (SIP) OPTIONS to detect the availability of the link from the local network element to the adjacent network element. During a call connection, the local network element selects an available adjacent network element to offer services according to the availability of the link to the adjacent network element. The method is able to improve the success ratio of control plane signaling connection, thus improve the reliability of the whole network. According to the idea of the adjacent network element load balancing selection, a proxy CSCF (P-CSCF) entity, a serving CSCF (S-CSCF) entity and a breakout gateway control function (BGCF) entity in the IMS respectively apply the load balancing method to select an interrogation CSCF (I-CSCF) entity, a BGCF entity or a media gateway control function (MGCF) entity.
The local network architecture of the ideas of the network element availability detection and the adjacent network element load balancing selection used in the IMS is shown in FIG. 1, in alive period of the P-CSCF entity 101, the P-CSCF entity 101 sends a SIP OPTIONS signaling at a preset time interval to the I-CSCF entities 102 which connect with the P-CSCF entity 101, and if a response signaling from one I-CSCF entity 102 is not received in a preset time period and the number of not receiving the response signaling surpasses a preset numerical value, then that I-CSCF entity 102 is considered as unavailable. Once a register signaling of one user equipment (UE) 103 needs to be out, in the current available I-CSCF entity set obtained by the availability detection result the P-CSCF entity 101 selects a suitable I-CSCF entity according to the load balancing strategy, and routes the register signaling to the selected I-CSCF entity. Similar to the process of a P-CSCF entity selecting an I-CSCF, in the IMS the processes of a S-CSCF entity selecting a BGCF entity and a BGCF entity selecting a MGCF entity can also use the abovementioned method.
The abovementioned method has the following problems that:
a P-CSCF entity can detect the availability of I-CSCF entities, but the I-CSCF entities cannot detect the availability of a P-CSCF entity, that is, the detection is not bi-directional;
if there is a P-CSCF entity and/or an I-CSCF entity adding in the IMS network, the configuration of all entities in the IMS network has to be modified; and
if in the IMS network the P-CSCF entity, the I-CSCF entity and the S-CSCF entity have a plurality of physical entities respectively, the load of the IMS network is increased due to a large number of SIP OPTIONS signalings for the network availability detection added in the network.